Osteoarthritis pain likely comes from other structures within the affected joint. For example, structures that change with osteoarthritis include:
Subchondral bone - This is the layer of bone just below the cartilage. When someone has osteoarthritis, there is increased blood flow and other changes that develop in the subchondral layer -- subchondral sclerosis (increased bone density), subchondral cysts (fluid-filled sacs which extrude from the joint), and increased pressure within the bone -- all of which may cause osteoarthritis pain.
Joint margin - There can be thickening of the joint capsule and the formation of osteophytes that may cause pain.
Capsule and synovium - There can be increased thickness of the synovium and mild inflammation at this site that causes pain.
Tendons and bursa - Tendinitis and bursitis occurring around a joint may cause pain, decreased range of motion, muscle wasting and muscle weakness.
The disease process associated with osteoarthritis is complicated. It's important to treat osteoarthritis pain and to get quick relief when possible, but it's also important to understand the source of the pain.
Source:
Osteoarthritis: Diagnosis. MerckMedicus. March 2001.
http://www.merckmedicus.com/pp/us/hcp/diseasemodules/osteoarthritis/diagnosis.jsp
